A communication method for data communication on a network is divided into a reliability-guaranteed protocol and an unreliable protocol, depending on whether the reliability of transmission data is guaranteed.
The reliability-guaranteed protocol indicates a protocol which retransmits a frame which was lost during transmission or not transmitted due to a communication trouble, using a response frame to a transmission frame. Thus, a receiver side checks the order of the frames and recombines the frames. Then, the receiver side checks a frame lost in the middle, and re-receives the corresponding frame, thereby receiving complete data. Representative examples of the reliability-guaranteed protocol may include TCP (Transmission Control Protocol).
The unreliable protocol does not guarantee the reliability of transmission like broadcasting, but one-sidedly transmits data. Representative examples of the unreliable protocol may include UDP (User Datagram Protocol).
Recently, with the rapid spread of wireless communication terminals, the wireless Internet environment has spread worldwide. However, the quality of the wireless Internet environment is yet lower than that of the wired network.
Furthermore, with the spread of cloud servers and the like, more and more global suppliers have tended to provide a service to global consumers, and the increase in number of routers between terminals during a communication process between the terminals has reduced the network quality. In particular, while the number of smart phones and network-aware devices is rapidly increased, the NAT (Network Address Translation) requirements of the routers have become complicated. Thus, problems related to the network quality have increased.
In the TCP capable of guaranteeing the reliability, the problem related to the network quality has been significantly improved by the efforts of network equipment suppliers for compatibility and stability. However, in the UDP which cannot guarantee the reliability, various errors occur.
Furthermore, a network router or switch does not transmit and receive data of which the size is equal to or more than an MTU size of approximately 1,300 bytes, but tends to discard the data. Thus, in order to transmit and receive a datagram of which the size is equal to or more than the MTU size, a transmission side fragments the datagram, assigns fragment serial numbers to the fragmented datagrams, and transmits the fragmented datagrams to a reception side through UDP. Then, the reception side receives the datagrams and defragments the received datagrams.
When a predetermined pattern occurs in transmission data, a specific firewall blocks the transmission data. Since a specific pattern may be generated by the above-described serial numbers, the specific firewall blocks the data.
Representative examples of the specific firewall may include ‘Great Firewall of China’ which is a super-sized firewall constructed by China.
Korean Patent Publication No. 10-2012-0068526 has disclosed a data transmission system and method for improving the reliability of a UDP network.
As illustrated in FIG. 1, the UDP data transmission system according to the related art is a message transmission system for providing a UDP-based reliable communication service in a communication system which includes IP multicasting or broadcasting for a plurality of receivers. Before the UDP data transmission system transmits data through UDP, an application service fragments a message according to a size of one packet, assigns serial numbers and a destination ID to the fragmented packets, and transmits the packets to a local network through multicasting. Then, a reception side determines whether the destination ID is identical to the ID of the reception side, and determines whether the message is partly omitted, through the assigned serial numbers. If necessary, the reception side transmits a control message to the transmission side, and re-receives an omitted packet, which makes it possible to improve the reliability.
However, the related art has the following problems.
When the reception side transmits the control message to the transmission side in order to re-receive the omitted packet, the same effect as TCP occurs. In other words, the real time flexibility which is a unique advantage of UDP becomes meaningless.
Furthermore, the transmission packets to which the destination ID and the serial numbers are added may form a specific pattern. Thus, when the transmission packets pass through the above-described specific firewall, the corresponding packets may be blocked.